The invention relates to a combustor, and, more particularly, to a gas turbine combustor having, on a head end, particularly of an annular combustion chamber, at least one fuel nozzle and at least one swirl device which can be adjusted as a function of the load for the supply of combustion air. The swirl device has, between profiles of a nozzle-coaxial annular body, radial/tangential apertures which are distributed uniformly along the circumference, and have a cross-section that is constant along its overall length, and into which inwardly extending fingers of a sleeve which can be adjusted with respect to the annular body engage.
In the case of modern combustors and combustion chamber designs for gas turbine engines, a combustion is endeavored that is as low as possible in pollutants, particularly in the primary zone of the combustion chamber. The important pollutants are: CO (carbon monoxide), NO.sub.x (nitrogen monoxide), C.sub.x H.sub.y (non-burned hydrocarbons) as well as C (carbon). It was found that a considerable reduction of all concerned pollutant emissions is achieved at a comparatively low combustion temperature of &lt;1,900.degree. K. in combination with a comparatively high proportion of air compared to the supplied fuel.
In addition, relatively low pollutant emissions require, among other things, a uniform processing of the fuel-air mixture to be supplied to the primary zone as well as a good degree of burn-out. This is particularly true in combination with combustors which operate by means of air support as "low-pressure systems" with a high fuel atomization quality and a partially wall-side (fuel film on sleeve) and aerodynamic fuel evaporation. In this case, local undesirable fuel enrichment which may cause the forming of soot should be avoided, among others.
A combustor of this type for combustion chambers of gas turbine engines is known, for example, from German Patent Document DE-PS 24 42 895. However, without exception, the known combustor has stationary, and therefore non-controllable swirl devices for the fed combustion air. No possibility is therefore indicated in this case to master different operating conditions, such as starting, full load, idling, cruising (stationary), in a manner that is as low in pollutants as possible with respect to the corresponding required variable fuel-air flow rates.
From German Patent Document DE-OS 24 60 740, a two-zone combustion chamber concept is known with a high-temperature first combustion zone which is rich in fuel and has an approximately stoichiometric combustion and with a low-temperature second or main combustion zone which is connected axially behind the first combustion zone, is low in fuel and is therefore as low as possible in pollutants.
In the known case, there are fuel injection nozzles which can only be controlled separately for the respective combustion zones. There is no primary air feeding that can be controlled in consideration of variable operating conditions with a view to a low-pollutant "cold" combustion. Furthermore, in the known case, no swirl devices are provided by which the primary air to be fed is provided with rotational swirls and the fuel-air mixture can be processed in a homogeneous manner and an aerodynamically stable reaction zone can be built up for the combustion. In addition, such a known two-zone combustion concept is high in constructional expenditures and relatively expensive while also requiring a relatively pronounced chamber volume and a large combustion chamber length.
Furthermore, in the interest of a low pollutant combustion, combustion chamber concepts which provide a "variable chamber geometry" in order to supply combustion air and possibly mixed air by way of holes of rows of holes are high in constructional expenditures, technically complex, susceptible to disturbances and expensive. The holes can be controlled in their cross-sections in that tube sections of the flame tube jacket of the combustion chamber can be displaced relative to one another in the axial or circumferential direction.
From European Patent Document EP-PS 0251895, an annular combustion chamber of a gas turbine engine is known which has, on the air-approach-side head end, several combustors distributed along the circumference. For a combustion that is low in pollutants, an "external" swirl device is assigned to each combustor. The swirl device can be regulated or blocked off with respect to the supply of a portion of the combustion air. A nozzle-central, axially fixed whirling device may be assigned to the "external" swirl device. Between radial wall portions of a nozzle-coaxial central body, the "external" swirl device is constructed with a radial inflow and with obliquely set apertures which are uniformly arranged along the circumference. The adjusting takes place by a screen which can be rotated on the outside on a central body in the circumferential direction and which has fingers on openings distributed along the circumference. The fingers, according to their length, project partly into the apertures and in intermediate positions of the screen. Each has an angular position which deviates from the apertures. In the intermediate positions of the screen which are decisive for the adjusting, in the known case, a pre-throttling of the air flow takes place in conjunction with an aerodynamic influencing which interferes with the natural given geometry of the apertures. In other words, in the manner of a separating diffusor flow, the respective circumferential component of the flow at the respective outlet of an aperture is clearly reduced, whereby the required swirl generating is considerably impaired. However, this is a significant disadvantage for a uniform turbulence development required during the whole operating condition and a resulting uniform combustion which is stable and low in pollutants.
There is therefore needed a combustor of the initially mentioned type in the case of which at least one swirl device permits the air flow rate operationally required for a combustion which is homogeneous and low in pollutants while a uniformly pronounced rotational whirl is maintained.
According to the invention, this need is met by a gas turbine combustor having, on a head end, particularly of an annular combustion chamber, at least one fuel nozzle and at least one swirl device which can be adjusted as a function of the load for the supply of combustion air. The swirl device has, between profiles of a nozzle-coaxial annular body, radial/tangential apertures which are distributed uniformly along the circumference, and have a cross-section that is constant along its overall length, and into which inwardly extending fingers of a sleeve which can be adjusted with respect to the annular body engage. The fingers engage by way of the sleeve in an axially displaceable manner in the apertures. The fingers are each arranged in parallel to axially spaced walls of the apertures which bound the maximal adjusting path and form duct walls of the apertures which move along by way of the sleeve. With respect to their width and length, the fingers are coordinated with the apertures in such a manner that, in intermediate positions, each finger adjusts with respect to the respective one wall a flow cross-section which is constant along the whole aperture length.
In the case of the invention, it is essential and important that, with respect to the swirl device, in all intermediate positions of the axially slidable sleeve, the existing geometry of the apertures is maintained with respect to the radial tangential flow. The fingers virtually form in each case a lateral wall of an aperture which is moved along with the sleeve in the axial direction and which is designed to be coordinated with respect to the circumferential width, height and length with the respective duct height and length. Preferably, the apertures may therefore in each case form a rectangular, square or rhombic duct cross-section, in which case the actual flow is in each case formed between the one movable wall and the locally exposed stationary wall sections of the apertures. Furthermore, according to the invention, the apertures may also be constructed or defined as ducts or slots. Thus, by way of the indicated characteristics, the swirl flow and therefore the desired rotational whirl geometry which shares in the responsibility of an optimal processing of the fuel-air mixture is not impaired in the different intermediate positions.
By means of the swirl device, the whole or a significant portion of the primary air can be supplied which is required for a combustion that is low in pollutants. In the case of only one controllable swirl body, the flow ducts or apertures would therefore have to have sufficiently large dimensions.
In an advantageous further development, the invention permits the combination of at least one controllable or adjustable swirl device with a stationary swirl device which makes available a constant air supply during the whole operating condition. The fuel supply is varied depending on the load condition, in which case an air supply is "superimposed" on the variable operating conditions which, while being adapted to the respective operating conditions, meets the air requirement with respect to a combustion that is low in pollutants. The latter air requirement may be adjusted, for example, as a function of an operationally increasing combustion temperature and/or pressure in the combustion chamber.
The invention includes the possibility of burning, for example, stoichiometrically, in certain engine conditions--as well as dependent upon the design and use spectrum of the engine--thus during the igniting and the start of the operation as well as, possibly, during an extreme full load, and burning--predominantly in the cruising operation--with a large amount of air and therefore in a manner that is low in pollutants.
The concerned swirl devices may generate approximately in the same direction or in mutually opposite directions rotational or mixed-air whirls which rotate with respect to the combustor axis or nozzle axis.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.